Atari 7800 just crapped out

[markronz]

So, for the first time in a long time, I just decided to hook up my Atari 7800. When I hit the power button the initial time the power light came on for about 1 second, and then the whole unit shut off and hasn't worked since. There seemed to be a barely detectable smell coming from the console as well. Pretty sure there was anyway. It's old (though in good condition) but it may just smell weird I suppose. Is there any common things that would fry inside one of these? I've read an awful lot today about people with power switch issues, but since mine did turn on initially, I didn't think that was my issue.

 

Any clues for me? I do have a power meter, although I really don't know how to use it. So if you have any tips that involve that, please be detailed. Any help would be appreciated! Thanks!

[AAirhart]

Check the power supply first, right where it connects to the system. Move it around a little, that wiring tends to break.

[markronz]

Thanks for the reply. I have been playing around with it a little. I did move around the connector and it didn't really seem to help anything. By all accounts the both the wiring and the port soldered onto the circuit board appear to be in good condition. I did open up the console and visually inspect it. The only thing that seemed weird to me was that the two dial like things in the middle of the board had a yellow glue looking substance on them. I touched them and the yellow stuff did come off very easily. Not sure if that is related at all... Any more ideas?

[+Mitch]

That was glue on the dials, it is not related to your power issue. Do you have a volt-meter? You need to check the voltage on the power supply, if it's good then you need to check the voltage on the voltage regulator.

 

Mitch

[markronz]

Thanks. I do have a power meter. Could you give me some more details on how to test both those using it? I'm not very familiar with the voltage meter and I'm not sure where I should be testing. Or if this information is noted somewhere I'm not aware of, could you point me to there?

[Jinks]

So the power light wont come on. plug it in and press power and move your finger left and right while holding down on the switch. might just be the power switch.(7800 common fault)

[MAC-42]

Could a smell possibly indicate a blown capacitor? Never had that happen (knock on my wood block head) so I don't know if there would be a smell, but just throwing that out there in case the simple faults don't pan out.

Edited July 3, 2013 by MAC-42

[captmorgandrinker]

If your power supply tests out ok, I have a bare console I could sell you if you want.

[chas10e]

I imagine follow the cuircuit through the console with your multimeter start with power supply itself , then connector inside then the switch

 

I haven't cracked open a 7800 yet ... I heard DO BE CAREFUL re-assembling it ... the screw pedestals are easily broken off if over-tightened

 

I'd use my nose also to try & tell what part "smoked"

[markronz]

Thanks for the replies everyone! What an active forum, very nice to see. My power supply checks out and measures at around 12 which is what I would suspect. I tried to measure the leads going into the power button and there was nothing there. So the power is not reaching the power button. Still, I tried pushing the power button and moving my finger left and right but that didn't help. As I mentioned before though, the unit did turn on just fine initially, albeit for only one second. But my point is that the power switch was working without issue. Just that something went wrong right afterwards. I tried to smell the circuit board now and I can't really smell anything that smells different than the rest. But what I smelled yesterday, the sort of burning smell that was coming from the console is gone. So that leads me to believe that something did burn out yesterday. Who knows what. I'm not sure I know how to really follow the power through the circuit board, so perhaps I ought to investigate getting a new board. If anyone has any other ideas for me to try, let me know. Otherwise, I guess I'll start moving on since I'm afraid this is beyond my skill level.

[tep392]

If you smelled something burnt, then there is a chance you can spot the bad component visually. Just look for any components that are discolored or look odd. Take some good photos and post them here. We'll go from there on next steps to troubleshoot.

[+Mitch]

Likely it is the voltage regulator. It's right behind the cart port attached to the large heat sink.

 

Mitch

[Blue Azure]

Ground (return) is the middle pin on the 3-pin voltage regulator that Mitch is talking about. One outside pin is the input (unregulated 12VDC) and the other pin, the output, should read about 5VDC. You can only measure voltages with the power pack connected to the wall, so be careful not to short anything inside the 7800 when you do this test. The power switch, S1, could be the culprit, except that you smelled a burning smell. You can check the switch with an ohmmmeter across the pins and press the button. The smell could be anything, a capacitor or an IC (integrated circuit). The power control chip is U10, the CD4013 dual D Flip Flop. It's CMOS and it could have blown but I doubt you'd smell that. A key Capacitor is 0.22uF, C55. If that's blown you won't get power on. Check solder especially on the regulator. There could be a cracked pad. You can check U10 for unregulated 5VDC across from VCC (pin 14) to ground pin 7, generally the pin 1 is labeled with a dimple. U10 has ground on pin 7 and 5VDC on pin 14. Starting with pin 1, count along the same edge of the device to pins 1,2,3,4,5,6,7. Pin 14 is diagonal across from pin 7. I'm assuming you're talking NTSC/USA. There is a schematic at atariage.com documents section, http://www.atariage.com/7800/archives/schematics_ntsc/ the U10 is located at the upper left. The power LED (CR2) is located in the middle upper part of the schematic.

 

Good luck

 

///blueman\\\

[markronz]

I think I'll have to take another look at this after the long holiday weekend. Thanks very very much for all the suggestions. Hopefully I can do some testing and narrow it down when I return!